The proposed research aims to investigate the regulatory mechanism used by LytTR Regulatory Systems (LRS) as well as explore a cell death pathway triggered by these systems in Streptococcus mutans. LRS are a newly described gene regulatory system that consists of a LytTR family transcription regulator and putative membrane protein inhibitor that antagonizes the function of this regulator. The goals of this project will b achieved in three aims by: 1) determining the inhibitory mechanism employed by LRS membrane proteins; 2) characterizing the components downstream of LRS responsible for mediating cell death; and 3) developing a therapeutic model of the LRS cell death pathway. 1) To determine how LRS membrane proteins function as inhibitors, we will examine three different mechanisms of inhibition: protein stability, posttranslational modification, and sequestration. Protein-protein interaction studies will determine whether LRS membrane proteins exert their function directly. 2) To characterize the mediators of cell death, we will use genetic techniques to determine the genes/pathways required for the lethal phenotype of a mutant strain that constitutively activates the LRS cell death pathway. 3) To assess the therapeutic potential of the LRS cell death pathway, we will test a positive feedback regulatory model between three S. mutans LRS. An inducible cell death system will be tested for functionality in in vitro and in vivo model systems. The goal of these studies is to create a model system for LRS function in Gram positive bacteria and to determine the potential utility of the LRS cell death pathway in inhibitin preformed biofilm communities.